In a UMTS (Universal Mobile Telecommunications System) network, attempts are made to optimize features of the system, which are based on W-CDMA (Wideband Code Division Multiple Access), by adopting HSDPA (High Speed Downlink Packet Access) and HSUPA (High Speed Uplink Packet Access), for the purposes of improving spectral efficiency and improving the data rates. With this UMTS network, LTE (Long-Term Evolution) is under study for the purposes of further increasing high-speed data rates, providing low delay, and so on (non-patent literature 1).
In a third-generation system, it is possible to achieve a transmission rate of maximum approximately 2 Mbps on the downlink by using a fixed band of approximately 5 MHz. In a system of the LTE system, it is possible to achieve a transmission rate of about maximum 300 Mbps on the downlink and about 75 Mbps on the uplink by using a variable band which ranges from 1.4 MHz to 20 MHz. In the UMTS network, successor systems to LTE are also under study for the purposes of achieving further broadbandization and higher speed (for example, which may be called LTE advanced or LTE enhancement (hereinafter referred to as “LTE-A”)).
In the downlink of the LTE system (for example, Rel-8 LTE), there is defined CRS (Cell-specific Reference Signal) that is associated with a cell ID. The CRS is used to demodulate user data and also used to measure downlink channel quality (CQI: Channel Quality Indicator) for scheduling and adaptive control, and so on. In the downlink of the LTE-A system (for example, Rel-10 LTE), CSI-RS (Channel State Information-Reference Signal) is under study, as a reference signal for measuring channel state information (CSI).